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Body Composition and Physical Performance 1992. Pp. 207-220. Washington, D.C. National Academy Press Sex Differences and Ethnic/Racial Differences in Body Size and Body Composition Stanley M. Garn SEX DIFFERENCES IN BODY SIZE AND BODY COMPOSITION At all ages, from the first trimester through the tenth decade, the man is the larger of the two chromosomal sexes, being longer and heavier and with a larger lean body weight (LBW). Even during childhood, when boys and girls are most alike dimensionally, the chromosomal XY is considerably larger than the chromosomal XX of the same physiologic (or skeletal) age. Because there is some increase in stature even after age 20 and some gain in the LBW through the midtwenties, the full expression of sex differences in dimensions and LBW is not evident until late. There are also sex differenc- es in fat weight (FW), although the woman is not necessarily fatter, either in absolute terms (FW) or even as a percentage of body weight (percent fat [% F]), as so commonly believed. In adulthood, the man is generally taller, by about 6 or 7 percent across the socioeconomic (SES) range and in different genetic populations. This stature excess is disproportionately expressed in the appendicular skeleton, a factor of considerable importance to vehicular design and to the design and operation of equipment and firearms and the location of controls. In adult- hood, the man generally has a larger LBW by a ratio of approximately 3:2 (for example, 61 kg or so versus 43 kg or so). This sex difference in LBW is reflected in the sex difference in basal energy requirements, in the caloric 207

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208 Stature STANLEY M. GARN TABLE 13-1 Distributions of Stature, Weight, Fat Weight, and Lean Body Weight in 30- to-39-year-old Tecumseh, Michigan Men and Women Lean Body Weighty Percent Weight Percent Fat Weight* Percent Percent cm Men Women kg Men Women kg Men Women kgMen Women 140 .0 .0 43 .0 4.1 4 .4.4 20 .0 .0 142 .0 .0 48 .4 13.5 6 3.14.1 25 .0 2.0 144 .0 .0 53 .8 14.3 8 4.25.3 30- .4 10.2 146 .0 .0 58 5.8 23.3 1 0 6.27.7 35 4 25.3 148 .0 .8 63 10.0 17.1 12 7.310.6 40 3.1 30.2 150 .0 1.2 68 15.4 10.2 14 7.38.5 45 14.2 20.0 152 .0 4.1 73 16.5 6.5 1 6 7.37.3 50 21.9 9.8 154 .0 7.3 78 18.5 4.5 18 9.69.3 55 28.1 .8 156 .0 8.2 83 16.2 3.3 20 8.57.3 60 23.1 1.2 158 .4 7.3 88 6.2 .4 22 9.26.9 65 6.5 .0 160 .8 13.5 93 6.2 .8 24 8.14.9 70 1.5 .0 162 1.9 16.3 98 1.5 .0 26 3.82.8 75 .8 .0 164 1.9 9.8 103 1.5 .4 28 5.06.5 80 .0 .4 166 3.5 12.2 108 1.2 1.6 30 6.94.5 85 .0 .0 168 6.5 6.5 1 13 .0 .0 32 4.63.3 170 10.4 6.1 34 5.02.8 172 1 1.9 3.3 36 1.5.8 1 74 1 3.5 1.2 3 8 1.52.0 1 76 1 5.0 1.6 40 .01.2 178 1 1.5 .4 42 .4.0 1 80 5.0 .0 44 .01.6 1 82 8.5 .0 46 .0.4 184 2.7 .0 48 .0.4 186 2.7 .0 50 .0.8 188 1.9 .0 52 .0.4 190 1.9 .0 54 .0.0 192 .0 .0 56 .0.0 194 .0 .0 58 .0.0 *Individually calculated from the regression of weight on four skinfolds. tTotal body weight (TBW) minus fat weight (FW). allowances set by the Food and Nutrition Board's (FNB) Committee on Di- etary Allowances (the Recommended Dietary Allowances the RDAs) and in caloric intakes actually reported in major nutritional surveys (Ten-State, NHANES I and II, the Tecumseh Community Health Survey, and so on). There is, of course, an overlap between the two sexes) in body size, LOW, FW, and also in skeletal weight (which will be discussed later). For . 1 . t For the discussions that follow, also see Figures 13-1 through 13-9 in the chapter appendix, which graphically present the sexual overlap for body and skeletal weight and size variables in men and women aged 40-49 years from the Tecumseh Community Health Survey.

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SEX, ETHNlCl7~Y AND BODY SIZEICOMPOSITION TABLE 13-2 Distributions of Bone Area, Cortical Area, and Skeletal Weight in 30-to-39-year-old Tecumseh, Michigan Men and Women 209 Bone Area (TA) Cortical Area (CA) Medullary Area (MA) Skeletal Weight (SW)* Percent Percent Percent mm Men Women mm Men Women mm Men Women g Percent Men Women 35 .0 4.1 20 .0 .4 0 .0 5.3 1400 .0 .8 40 .0 12.8 25 .0 .0 1 2.8 7.8 1900 .0 9.1 45 1.2 24.8 30 .0 1.2 2 3.6 11.9 2400 .8 42.3 50 4.4 22.3 35 .0 11.5 3 4.4 12.3 2900 7.6 32.8 55 4.8 21.1 40 .4 28.0 4 5.2 11.1 3400 16.7 11.2 60 7.6 6.2 45 4.8 30.5 5 6.0 13.2 3900 29.1 3.3 65 16.4 6.6 50 8.8 16.9 6 5.6 10.3 4400 22.3 .4 70 20.0 2.1 55 17.9 7.8 7 11.6 10.7 4900 15.5 .0 75 15.2 .0 60 23.9 2.5 8 6.8 3.3 5400 7.2 .0 80 13.2 .0 65 20.7 1.2 9 5.6 2.9 5900 .8 .0 85 6.8 .0 70 13.1 .0 10 5.2 2.1 6400 .0 .0 90 4.8 .0 75 6.4 .0 11 6.4 2.1 95 3.6 .0 80 2.4 .0 12 7.2 1.6 100 2.0 .0 85 1.6 .0 13 6.4 2.9 14 4.8 .8 15 4.0 1.2 16 1.2 .4 17 2.0 .0 18 4.8 .0 19 .4 .0 20 1.6 .0 21 .8 .0 22 2.0 .0 23 .4 .0 24 .4 .0 25 .4 .0 *SW = 0.969 CA x L or 0.7611 (T2 _ M2)L, where: SW = skeletal weight; CA = cortical area; L = bone length; T = total width; and M = medullary width. weight and FW, the overlap is considerable (see Tables 13-1 and 13-21; the overlap area is of importance to military planning and materiel tariffs from several points of view. Moreover the actual or operational overlap may be greater or less depending on recruitment standards, self-selection of volun- teers, and selective dropout rates. If women who volunteer for service are self-selected for greater stature or for a larger LOW, as is likely, or if training programs and the service academies further select, then the women in service will exceed their total-population (civilian) counterparts in body size and robust build. At the same time, entry standards, self-selection, and attrition during basic training may also exclude the smaller and less-mus

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210 STANLEY M. GARN cled men, thereby decreasing the dimensional and ponderal overlap between the sexes. Furthermore, there is the question (which cannot be properly answered here) as to how much basic training and in-service physical training may modify, decrease, or even increase sex differences in muscle mass of male and female volunteers. Both sexes do gain in muscle mass during such training. There is a common belief that men, with their testosterone, gain disproportionately more muscle with training, but with joint-sex exercise programs and suitable motivation, women may gain as much LOW propor- tionately although they may be liable to exercise-induced amenorrhea due to decreased estrogenic levels. Skeletal weight, bone sizes, and amounts of tissue bone all differ be- tween the sexes even more than LBW differs. So, the calcium content of the male skeleton approximates 1,000 g as compared with perhaps 750 g for the female skeleton, and the skeletal weight ratio is then on the order of 4:3. Moreover the "overlap" in skeletal size or skeletal weight may be well under 30 percent (see Table 13-2~. With smaller skeletons, less tissue bone, smaller bone widths, and smaller cortical bone area (CA) one might expect bone fracture rates to be higher in women than in men, an expectation of potential importance to the military both with respect to training injuries and to vehicular accidents. However in actual experience, civilian fracture rates are higher for men than for women in the age range of 20 to 40 years. Only after the fifth decade does the fracture rate in women begin to exceed the fracture rate in men. Why men under 45 years of age fracture more and women aged 20 to 45 fracture less is not known, although men are more often engaged in high- risk construction occupations, and they are more accident-prone when they drive (and they do drive more miles). However, the smaller bones of young adult women do not necessarily result in a higher fracture rate in civilian life. Again, the overlap in bone size and bone area between men and women must be considered as shown in Table 13-2. What the actual os seous overlap is in enlisted men and women and those at noncommissioned officer and officer ranks remains to be ascertained. Also to be ascertained is the incidence of forearm (Colles' and Parry) fractures in military-age individuals of both sexes. The question of sex differences in fat weight (FW) and percent fat (%F) is complicated, and some of the answers are surprising. That women gener- ally do have a thicker panniculus of outer fat is well known, but this is not always the case; some women have less outer fat than men do. When FW is measured, the two sexes are often quite similar, a fact that is not well appreciated (Table 13-31. Yet percent fat (%F) is generally higher in wom- en because FW may be the same, but total body weight (TBW) is consider- ably less. Even so, the overlap in percent BF is considerable.

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SEX, ETHNICITY AND BODY SIZEICOMPOSITION TABLE 13-3 Correspondences Between Male and Female Percentiles for Size and Body Composition in 30-to-39-year-old Tecumseh, Michigan Men and Women Male Centiles Corresponding to Women's Fiftieth Women's Eighty-fifth Measure Percentile Percentile Stature Weight Fat weight Lean body weight Bone area (TA) Cortical area (CA) 2.0 7.0 45.0 2.3 3.4 2.0 Medullary area (MA) 34.4 Skeletal weight (SW) 0.8 13.1 40.6 88.5 18.1 10.4 14.0 48.0 8.4 NOTE: This table is to be read in the following manner. The fiftieth percentile for stature in women corresponds to the second percentile in men. The eighty-fifth percentile for stature in women corresponds to the thirteenth percentile for men. Note that the sexes are most alike in fat weight and skeletal weight. 211 As a complication, fatness either fat thickness or FW is inversely related to education in women at a rate of nearly -O.S kg per year of educa- tion, which suggests that how fat a woman is depends largely on her socio- economic status. If the military recruits only women of high school educa- tion (12 years) or beyond, their fatness may be lower than the average, and even lower than that for men of similar educational level. Moreover, leaner women may self-select for military service, and fatter women may be ex- cluded from advancement or continuation in the service. The point here is that the appropriate level of fatness for service-oriented women cannot be prejudged from total-population or national-probability FW distributions. A further point about fatness is derived from family-line studies. There are large familial differences in fatness levels. Daughters of lean families are far leaner than sons of obese families. This finding again opens the question as to whether women are necessarily or inherently fatter than men even though on the average they are. In the civilian population, fat weight (FW) increases regularly and lin- early with age at a rate of approximately 0.5 kg/year in women. However, this age-related increase is not necessarily a biological "given," occurring far less in the affluent and somewhat more in the poor. So an age-related increase in fatness is not necessarily the universal rule. Indeed in some third world countries fatness actually decreases with age. With one excep

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212 STANLEY M. GARN lion, one might even consider a no-increase rule for FW in the military as being both desirable and practical. The exception has to do with pregnancy, where higher levels of fatness are advantageous for fetal growth and devel- opment (see below, "Relevant Epidemiologic Aspects of Fatness and Fit- ness"~. ETHNIC AND RACIAL DIFFERENCES IN BODY MASS AND BODY COMPOSITION Although many ethnic and racial differences in size and body composi- tion have been claimed and some documented, it is quite difficult to sepa- rate most such differences from years of residence in the United States and from socioeconomic status (SES). Male and female immigrants of recent arrival tend to be smaller, poorer, and shorter, but the immigrant women soon become fatter and more often obese. However, both size and body composition change as ratios of income to needs improve. Such differences between immigrants and their Fit progeny pose problems in setting military standards exactly the same problems that were encountered by the first Committee on Military Anthropometry in 1917. That wartime committee recommended a lowering of stature and weight standards so that recent immigrants from Russia and the Austro-Hungarian Empire would not be subjected to the height and weight standards established for so-called "na- tive Americans". In recent years there has been much litigation concerning weight and weight-height standards for airline stewardesses, oil industry workers, post- al workers, and even Sears Roebuck shipping clerks. Courts have ruled that military, National Center for Health Statistics (NCHS), and the Metropoli- tan Life Table standards for size or weight-for-height are not necessarily appropriate for Mexican-Americans, Puerto Ricans, Colombians, and oth- ers. Even people with extremes of weight-for-height have been ruled as employable as long as those individuals can do their jobs, such as lifting 80-pound mail sacks. Most immigrants from Meso-America, South America, the West Indies, and the Philippines and Asia are shorter than the NCHS norms and conse- quently have a smaller lean body weight (LBW). Such individuals and their foreign-born children are small by American military standards and may be accorded restricted military duties or excluded from certain classes of troops. With increased length of stay in the United States, and now in the F2 generation, these immigrants more nearly parallel other Americans. American Blacks (Americans of largely African ancestry) pose an in- triguing problem, for they are taller as children and adolescents (ages 2 through 14) than are Whites of comparable age. As adults they average close to the U.S. means, may be taller than other Americans of comparable

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SEX, ETtINICI7~Y AND BODY SIZEICOMPOSITION 213 socioeconomic status, and with an excess above the ninety-fifth percentile limits. American Blacks (or African-Americans) also appear to have a slightly higher LBW, which indicates a larger muscle mass. Best documented and of considerable interest is the larger bone mass in African-Americans. This difference is apparent in the fetal condition, dur- ing infancy and childhood, and continuing through the tenth decade of life. This larger skeletal mass (larger bone diameters and larger volumes of cor- tical bone) may be one factor behind the lower fracture rates for adult Blacks of both sexes. However the larger skeletal masses (bone weights and tissue bone volumes) may not be translatable into duty assignments. Much attention has been given in the literature to the greater fatness of Black women, Hispanic women, Native American women, and so on. In- deed, fatness and obesity in Native American women have been attributed to population-specific "thrifty" genes. However this greater fatness appears to be more of a poverty-related phenomenon than a true genetic difference. Poor White women are fatter than affluent White women, and fatness de- creases linearly with both years of education and family income. Fat weight (FW) also decreases with increasing socioeconomic status in Black women. There may be good political reasons to accept higher-weight and fatter Black, Meso-American, and Native American women into military service, but there can be no assumption that such differences are necessarily genetic. Studies have also claimed racial and ethnic differences in fat place- ment, fat distribution, or fat "patterning". Expressed as ratios (for example, triceps:subscapular), such differences do exist, but these ratios are inherent- ly fatness dependent. The triceps:abdominal circumferential ratio is much higher in lean individuals and much lower in the obese, so that some racial differences in fat placement may be no more than simple differences in the amount of fat. Of course, clothing and other covering equipment may be affected by such differences, but differences in relative leg length or hand size or foot size relative to stature may be more important. For constant stature, hand lengths and foot lengths (or metacarpal lengths and tarsal lengths) are approximately 1 standard deviation (SD) longer in American Blacks, whatever their nutritional status. There are real and considerable ethnic and racial differences in body size and body composition, and in an emergency or crisis situation they may be taken into account. However, many of these differences (except the greater LBW and bone weight in African-Americans) disappear with time, affluence, and generational changes. The greater fatness of low-income women of all ancestries is very real and bears on recruitment and enlistment standards, but it is not necessarily genetic. How such differences are ad- dressed involves political decisions, which may be discriminatory, however decided. It is probably beyond the scope of this advisory group to attempt ethnic-specific recommendations.

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214 STANLEY M. GARN RELEVANT EPIDEMIOLOGIC ASPECTS OF FATNESS AND FITNESS The weight of fat (FW) and therefore the percent of fat (OF) is control- lable both by caloric restriction and by increasing energy expenditure. This fact is important both with respect to field performance and to long-term mortality and morbidity. Controlling FW or percent F affects field perfor- mance over the short term and affects the development of atherosclerosis, coronary artery disease, diabetes, and hypertension later on. However, existing recommendations regarding the ideal, suggested, or optimal weight of fat are complicated by the nonlinear relationship between FW and age-specific mortality. At the upper end of the J-shaped curve, both morbidity and mortality rise with increasing levels of fatness. In contrast, morbidity and mortality also increase at the bottom end of the curve, where diseases of the respiratory system, including lung cancer, pre- dominate. Very lean individuals of either sex are clinically anorectic and at greater long-term risk. risk. Very fat individuals are also at greater long-term Low fat weights in women are of concern if they are associated with amenorrhea, and premature bone loss is likely for this group. Women athletes may find such low fat levels advantageous in the short term be- cause it frees them from the inconveniences of menstruation. However, the premature onset of bone loss and involutional osteoporosis in these women might then be claimed as a service-related disability. Furthermore, the ideal level of fatness associated with ideal fitness in women is far less than the level of fatness associated with optimal fetal growth and survival. Too lean a mother may be at greater risk for fetal loss, premature delivery, low birth weight, and increased neonatal mortality. Because a low prepregnancy weight (PPW) can be compensated for by a greater pregnancy weight gain, this aspect of body composition also merits atten- tion in military service. The long-term consequences of differences in FW also merit consider- ation. Because the Veterans Administration bears the cost of diseases asso- ciated with excessive fatness, body composition long after separation from service may well be an extended task of this conference. Pregnancy and pregnancy-associated risks are not necessarily part of the assigned mission, but body composition is important during pregnancy; too little fat is a risk factor with respect to pregnancy outcomes, and insufficient weight or fat may be a life-long risk-factor. Concerns of the military in the past were relatively short-term, relating to the ability of draftees and recruits to perform assigned tasks after entry into the services. Body size and bodily proportions also had some bearing on the design of equipment and on the number of sizes to be stocked.

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SEX, ETHNICITY AND BODY SIZEICOMPOSITION 215 Concerns now include changes in body composition during extended peri- ods of service up to 2 decades and more and fatness control to meet service standards. Moreover, there are the long-term implications both to service-induced disabilities and to the cost of medical care long after sepa- ration from the services. If the services are to be equal-opportunity em- ployers, they must accommodate racial and ethnic differences in size and body composition, including Vietnamese and Hispanics from southern Tex- as, California, and Florida. Looking to the future, there are the costs of hospitalization and medical care for those with excessive fatness and claims for service-induced disabilities. Even the children of those now in the service may seek compensation for excessive physical demands on their parents or for their own premature birth if their mothers were allowed to be too lean when they were in utero. ACKNOWLEDGMENTS All tabulations for age 30-39 year old men and women were specially calculated for this paper by Timothy V. E. Sullivan using raw data from the Tecumseh, Michigan Community Health Survey, including radiogrammetic measurements made under contract 53-3K06-5-10 with the Human Nutri- tion Research Center on Aging. Graphic representations for the 40-49 year old age group in Figures 13-1 through 13-9 in the chapter appendix use superimposed transparencies made from computer-generated histograms for men and women separately. APPENDIX The following figures were generated from superimposed transparen- cies made separately for men and women from computer-generated histo- grams. Data from the Tecumseh, Michigan Community Health Survey for individuals aged 40-49 were used throughout and thus provide comparative information for sexual overlap with the data from the same population on individuals aged 30-39 presented in Tables 13-1 through 13-3.

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216 4 oooo ~ X 6 . 0000 coax 8 . 0000 +~8 10. OOO+~.XXXXX 12 . 000 +0000OO 14. ~ +0000000000 16 . 000 1R . ~ 20. 2 2 . 000 2 4 . 000 26 . 000 ~ 2B . 000 ~686600eX X 30 000 +~8000 32 . 000 ~aBBHOor)O 34 . 000 +~)0 36 . (I 4~H X X 38 . 000 ~ 00 40.000 48~0 4 2 000 ~ 000(~000 44 . 4 6 . 000 4 ~ . 50 5 2 . 000 5 4 . 000 56 . 000 58 . 000 ~ en000000000000 ~60~068~80X X X +~000000sex x ~ ~0 lox x ~ODOOD00008XXXX ~0 +oo so +O + FAT WEIGHT MALE~40-49)-X FEMALE~4~49)-O FIGURE 13-1 Distribution of fat weight (FW) in kilograms (kg) in fifth decade (40-49 y) men (O) and women (X), where each X or 0 = 1 person. Note the completely overlapping distributions of FW in fifth decade men and women. A1- though percent body fat does differ markedly between the sexes, because of the larger body weight in men, the distribution of fat weight is similar. 43 000 +~8 48.000 +0000000000000 53.000 +800000000000000000000000 58.000 +~0000000000000000000000000 63.000 +~.ab6~OOOOOOOOOO 68.000 +~_/XXXXXXX 73 000 +~.e66~8x X X Y X X 78.000 +~.o.6X XXXXX:XX.Y/X Y 83.000 +~-~6XXXXXXXXXXXXXXX 88.000 +.e~xxxxxxxxxxxx 93.000 +~00 X X 98.000 ~XXXXXX 103.00 108.00 't3.00 +O +00 VVEIGHT MALE~40-49)-X FEMALE~40-49)-O FIGURE 13-2 Distribution of body weight in kilograms (kg) for fifth decade (40- 49 y) men (O) and women (X), where each X or 0 = 1 person. Note the overlapping distributions of weight in men and women. Because the fat-free weight of men is considerably larger than that of women, there is some bimodality in the body weight distribution, and this is especially apparent at the higher income levels.

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217 AX +o +f)o +O +O + 20 . 000 2 5 . 000 30 000 3 5 . 000 40 000 4 5 . 000 50 . 000 55.000 60 . 000 65 . 000 70 . 000 7 5 . 000 80 . 000 8 5 . 000 4 000 15 00(3 1 6 0(,'0 17.C~C) +O t 8 . OC~ +61~00 19. ~ +~00000 20 em> +~ses 2 1 . 00(? +~.OoOoooooo 2 2 000 +60066860000000 23.000 +~8101~800000000000000 2 ~ . 000 +60~800~606 X X X X X 2 5 . 000 ~ 8808666~ X x x x ~ 26 . 000 +~8XXXXXXXx ~ 7 . 000 +~R x ~ x ~ 28 .000 +~4101OlIIXXXXXXXxXX 2 9 . onto +~H x ~ x x 30.CX)O +~8 31 ooo +08800t)o 32.000 +600 33 000 AX 34 000 +0 35 000 ~ 3G 000 +oo 37 000 3 8 . 0<)0 3 9 . 00O 40 000 41. 42.OOV 43.000 44.000 45 Or9() 46.0~O 47.C`xxxxxxxxxxxxxxxxxxxxxx xxxxxXXXxXxxxxXXXXXxXXXX +~eyxxxxxxx XX xX FAT FREE WEIGHT MALE~40-49)-X FEMALE~40-49)-O FIGURE 13-4 Distribution of fat-free weight (FFW) in kilograms (kg) for fifth decade (40-49 y) men (X) and women (O), where each X or 0 = 1 person. Note that FFW shows considerable bimodality (or sexual dimorphism) in distribution because the ratio of FFW in men to women is 3:2. This dimorphism in FFW is reflected in sex differences in caloric intake and total energy expenditure.

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218 + 140.00 142.00 144 00 14fi 00 14 ~ .00 150.00 152.00 ~ sA . 00 156.00 158.00 16O GO 162.00 . - 1 ~ 4.00 *~8Q'()OO 16fi 00 *~'RR~()~0 68 00 *NS4SIN IIRRN~ x ~ 70. 00 1 72 00 74.00 176 . oo 178 Go 1flC). O0 ~ ~ 2.00 1 ~ 4.00 186.00 1 R8.00 1 90 . 00 192.00 1 94 . Go ~0 +C) +()o +000000 +000000000 +000000000000000000 +8OOOOOOOOOGOC)r]()OOOO +coooooooonor)()o(~ooooooooon +~8000000~0~)00 HEIR MALE~40-49)-X FEMALE~40-49)-O ~ , . . +~8QQO +~.XXXXXXXXXXXXXXXX XXXXXXX +XXXXXXXXXXXXX +.XXXXXX +X XX X X XX X X X X XXXXX ~XXXXXXXXXXXXX + X X X X X X X +XX AX +X XXX FIGURE l 3-5 Distribution of height in centimeters (cm) for fifth decade (40-49 y) men (X) and women (O), where each X or 0 = l person. Although the percentage difference in stat- ure is small only 7 percent or so- male and female statures show very little distributional overlap, a fact that has consid- erable bearing on equipment design, materiel tariffs, and pur- chasing schedules. O . ~ 000 ~ .0000 +80000000000000 2 0000 +DDDOOOOOOOOOCOOOOOOOOO 3.0000 +088000000000000000000000 4.0000 t D.~8OOOOOOO .0000 +.DDODDDOOOOooooooooo . ~+~06~0000 7 0000 +~eXXXXXXXX a, ~t8888~.X X X . ~+~8XXXXXXX 10. ~+~8XXXXX ~ ~ . ~+~68XXXXXXXXXXXX FIGURE 13-6 Distribution of ~ ~ 000 + xxxxxx medullary cavity area in mini- ~ ~ 000 ~ x x x x meters (mm) for fifth decade (40- ~ ~ . Too +.x x x 49 y) men (X) and women (Oy, 16 000 +6x x where each X or 0 = 1 person. ~ 7 000 ox 1 ~ . ~ X X x MEDULLARY AREA Note that there is considerable 18 000 ax MALE~4~49)-X overlap between the sexes in med- :20 . 000 ~ Y x FEMALE~4~49)-O ullary cavity area, although the 2 ~ .000 fix men, with greater hematopoiet- 22 000 2 3 . Coo 1C capacity, do have larger 2 ~ OoO amounts of red marrow. 25 .000

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219 20.000 2S . 000 30 000 IS . 000 40.~ US COO 50 . 000 55 000 CO . 000 C5 000 70 000 7 S 000 e0 . 000 BS . +00000 +0000000~000~000000000 +00000~0000000000000000-0000000000000 +~80~040000000000000000000000000000000 +~-00000 +~ -XYXXXXXXXXXXXXX +~0XXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXX ~XXXXXXXXXXXX +8XXXXXX>`XXX8~.IXX +yXXxxx XX CORTICAL AREA MALE~40-49)-X FEMALE~40-49)0 FIGURE 13-7 Distribution of cortical area in millimeters (mm) for fifth decade (40-49 y) men (X) and women (O), where each X or 0 = 1 person. Note that there is considerable sexual dimorphism in the cortical area. The overlap is small less than 15 percent because men have far more tissue bone. 3 5 000 40. 000 ~ 5 . 50 . 000 5 5 . 000 60 . 000 6 5 . 000 70 . 000 7 5 . 000 80.~ 8 5 . 000 so . ooo 9 5 . ooo 1 00 . 00 +0000000 +000000000000000000000000~0 +~000000000000000000000000~0000 +~00000~00000000000000000000000000000000 +~ 000000000000 -XXXXX + _ XXXXXXXXXXX +- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX "XXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXX XXXXXXXXXXX TOTAL AREA X X X X MALE~4~49)-X FEMALE~4~49)-0 FlOURE 13-S Distribution of total bone area in millimeters (mm) in fifth decade (40-49 y) men (X) and women (O), where each X or 0 = 1 person. Note that when total bone area is taken into account there is even further sexual dimorphism than for cortical area alone. The male skeleton possesses greater impact resistance than the female skeleton. This is especially true in the forearm where relatively light trauma such as falling-can result in a Colles or Parry fracture.

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220 S~FLETAl WEIGHT S4(~()() +0000 BRALESS Sl()().() +0OOOcOOOOOOOOOOO FE-ALES-o 49()().() ~ooooooooooooooooooooo 4('()()() +600000000000000 ~ 0000000000000~ 000000 4-~(~(~() +0000000000000000000000000000000000 4(~()(~.() +~800000 37(~.() HEX 34~)~}(} +~8XXXXXXXXXXXXXX'XX `31()~).~} ~XXXXXXXXXXXXxXXXXXXXXX 2X()(~.(} +aXXXXXXXXXXXXXXXXXX 25~)~).() ~XXXXXXXXXXXXXXXXXXXX 22~)~).~) ~XXXXXXXXXXX, 19()().(' ~XXXXXXXXXX 1 6(~(~.() +.X 1 3(~(~.() ~ X X 1 ()()().() ~ X X FIGURE 13-9 Distribution of skeletal weight in grams (g) for fifth decade (40-49 y) men (X) and women (0), where each X or 0 = 1 person. Note that the skeletal weight distributions in men and women are most different with very little overlap. Skeletal weight thus sums, in effect, the distributional properties of stature and the fat-free weight. The sex difference in skeletal weight plays an important role in human identification in mass disasters and skeletal weight alone affords close to 90 percent sex discrimination.